This invention relates to apparatus for, and methods of, irradiating articles such as food, drugs and medical instruments and implements. The invention particularly relates to apparatus for, and methods of, applying radiation to articles of different dimensions or to batches or stacks of articles of the same or different dimensions in a manner such that substantially all of the radiation is used to sterilize the articles and such that all of the positions of the articles receive proper amounts of irradiation.
It has been known for some time that drugs and medical instruments and implements have to be sterilized so that they will not cause patients to become ill from harmful bacteria when they are applied to the patients. Systems have accordingly been provided for sterilizing drugs and medical instruments and implements. The drugs and the medical instruments and implements have then been stored in sterilized packages until they have been ready to be used.
In recent years, it has been discovered that foods can carry harmful bacteria if they are not processed properly or, even if they are processed properly, that the foods can harbor such harmful bacteria if they are not stored properly or retained under proper environmental conditions such as temperature. Some of these harmful bacteria can even be deadly.
For example, harmful bacteria have been discovered in recent years in hamburgers by one of the large hamburger chains. Such harmful bacteria have caused a number of purchasers of hamburgers from stores in the chain to become sick. As a result of this incident and several other similar incidents, it is now recommended that hamburgers should be cooked to at least a medium state rather than a medium rare or rare state.
Similarly, harmful bacteria have been found to exist in many chickens that are sold to the public. As a result of a number of incidents which have recently occurred, it is now recommended that all chickens be cooked so that no blood is visible in the cooked chickens.
To prevent incidents such as discussed in the previous paragraphs from occurring, various industries have now started to irradiate the foods that are sold to the public. This is true, for example, of hamburgers and chickens. It is also true of fruits, particularly fruits which are imported from foreign countries. Radiation has also been used for sprout inhibition, shelf life extension and modification in the properties of materials.
In previous years, gamma rays have generally been the preferred medium for irradiating articles. The gamma rays have been obtained from a suitable material such as cobalt and have been directed to the articles to be irradiated. The use of gamma rays has provided certain disadvantages. One disadvantage is that irradiation by gamma rays is slow. Another disadvantage is that irradiation by gamma rays is not precise. This results from the fact that the strength of the source (e.g. cobalt) of the gamma rays decreases over a period of time and that the gamma rays cannot be directed in a sharp beam to the articles to be sterilized. This prevents all of the gamma rays from being useful in irradiating the articles.
In recent years, electron beams have been directed to articles to irradiate the articles. Electron beams have certain advantages over the prior use of gamma rays to irradiate articles. One advantage is that irradiation by electron beams is fast. Another advantage is that irradiation by electron beams is relatively precise because the strength of the electron beam remains substantially constant even when the electron beam continues to be generated over a long period of time.
Irradiation by electron beams has a limitation which sometimes may be significant. Electrons in the electron beams have mass. As the electrons in the beam travel through the article to irradiate the article, they are slowed and eventually stopped by the mass of the article. This limits the thickness of articles which can be effectively irradiated by electron beams.
X-rays have been used to irradiate articles. X-rays are advantageous in that they have no mass. The x-rays are in the form of electromagnetic energy which penetrates the articles to be sterilized. Since the x-rays have no mass, they are effective in irradiating articles with increased thicknesses. These significant thicknesses are considerably greater than the thicknesses of the articles which can be irradiated by other forms of energy such as electron beams.
There is one disadvantage, among others, in the use of x-rays to irradiate an article. This results from the fact that a considerable amount of energy remains in the x-rays after the x-rays have passed through the article. The energy remaining in the x-rays after the passage of the x-rays through the article is wasted because it has not been used for any useful purpose. Co-pending U.S. patent application Ser. No. 09/753,287 filed by applicants on Dec. 29, 2000 for a System for, and Method of, Irradiating Articles With X-Ray Beam and assigned of record to the assignee of record of this application discloses and claims a system for utilizing substantially all of the energy from the x-rays to irradiate articles.
There is another disadvantage in the use of x-rays to irradiate articles. The x-rays are generally produced by directing electrons to a converter which converts the electrons to x-rays. However, instead of constituting a focused beam as in the case of the electrons, the x-rays travel in different directions from the converter. A significant percentage of the x-rays move past the articles being irradiated without passing into the articles. This results in an inefficiency in the operation of the system since these x-rays do not provide any irradiation of the articles.
The processing inefficiency becomes particularly pronounced when the system is used with articles of different sizes. When the articles are relatively small, an increased amount of the radiation from the source moves past the articles without passing into the articles. When the articles are relatively large, not all of the volume in the articles receives a sufficient amount of x-rays from the source to become properly sterilized.
This invention provides a system for, and method of, passing radiation to an article so that an increase percentage of the x-rays passes into the article and the article becomes properly processed by the radiation. The system and method of this invention accomplish this by varying the distance between the position of generating the radiation and the position of individual articles, this variation being dependent upon changes in dimensions of the articles relative to the dimensions of other articles. In one preferred embodiment, the radiation source is displaced toward or away from the articles by a distance dependent upon the changes in the dimensions of the individual articles relative to the dimensions of the other articles.
In another preferred embodiment, the articles are moved on conveyors toward or away from the radiation source by a distance dependent upon the changes in the dimension of the individual articles relative to the dimensions of the other articles. In a third preferred embodiment, the individual articles are moved on the conveyor in a direction to vary the distance between the articles and the source of radiation.
Instead of processing a single article at any one time, the system may simultaneously process a plurality of articles which are disposed in a batch or in a stacked relationship.
In the preferred embodiments of the invention articles move on a conveyor mechanism in a first direction past a radiation source for a processing of the articles by radiation (e.g. gamma rays, electron beam or x-rays). The radiation moves in a second direction substantially perpendicular to the direction of movement of the conveyor. However, the radiation often has a component of movement in a direction perpendicular to the second direction. In effect, the radiation is scattered as a result of this perpendicular component of movement. Some radiation may move in the transverse direction past the articles without irradiating the articles. The distance between the radiation source and the articles on the conveyor mechanism may be adjusted to maximize the movement of the radiation to position in the article and to minimize the amount of the radiation which does not pass into the articles.
The adjustment may be made by (1) adjusting the position of the radiation source in a particular direction constituting the direction of the radiation source or (2) actuating an individual one of a plurality of conveyors for moving the articles past the radiation source, each conveyor being separated from the radiation by a distance different from the distance of the other conveyors from the radiation source, or (3) repositioning the articles on the conveyor in the particular direction. The distance between the radiation source and the conveyor mechanism may be varied dependent upon the variations in the dimension of the articles in a direction substantially perpendicular to (a) the direction of the radiation source and (b) the path of movement of the articles on the conveyor mechanism. Instead of irradiating a single article at any one time, the system may simultaneously irradiate a batch or stack of articles of the same or different sizes. It should be appreciated that the radiation source may be considered to include a converter for converting an electron beam to x-rays.